It is estimated that ______ square km land has been converted to unproductive deserts in the last 50 years:

A. 3.7 million
B. 3.8 million
C. 3.9 million
D. 4 million

The correct answer to the question: "It is estimated that ______ square km land has been converted to unproductive deserts in the last 50 years:" is "3.7 million ".